Methods of cleaning copper surfaces in the manufacture of printed circuit boards

Abstract

The present invention sets forth an improved method of microetching a metal substrate by contacting the substrate with an aqueous composition comprising a sodium persulfate or hydrogen peroxide oxidizing agent, acid, and one or more additives. When the oxidizing agent is sodium persulfate, the one or more additives generally comprise an aliphatic saturated dicarboxylic acid. When the oxidizing agent is hydrogen peroxide, the one or more additives generally comprise a stabilizer and amino tris(methylene phosphonic acid).

Description

FIELD OF THE INVENTION [0001] The invention relates to improved methods of cleaning metal surfaces during the production of printed circuit boards. BACKGROUND OF THE INVENTION [0002] Printed wiring boards (also known as printed circuit boards or PWB's) are generally laminated materials comprised of two or more plates or foils of copper, which are separated from each other by a layer of nonconducting material. Although copper is generally used as the electroplating metal in printed wiring boards, those skilled in the art will recognize that other metals such as nickel, gold, palladium, silver and the like can also be electroplated. The nonconducting layer or layers are preferably an organic material such as an epoxy resin impregnated with glass fibers, but may also comprise thermosetting resins, thermoplastic resins, and mixtures thereof, with or without reinforcing materials such as fiberglass and fillers. [0003] In many printed wiring board designs, the electrical pathway or patter...

AI Technical Summary

Benefits of technology

[0023] The inventors have surprisingly discovered that an aliphatic saturated dicarboxylic acid, especially glutaric acid, can be added to a sodium persulfate-based microetching solution to increase the cleaning capability of the solution without leaving a film on the treated copper surface and without the environmental concerns of the additives of the prior art. Furthermore, the improved microetchant of the invention advantageously reduces the etch rate on the copper surfaces.

Problems solved by technology

The carbon black and graphite dispersions on the PWB not only coat the drilled hole surfaces, which is desirable, but also entirely coat the copper plate or foil surfaces, which is undesirable.

The drawback to the use of these methods is that they contribute to a less clean copper surface, thereby increasing the number of defects due to carbon residues.

However, citric acid can leave a film on the copper surface, which can cause dry film lock (ie. inability to develop) and poor copper / copper adhesion.

In addition, since citric acid is a chelator, waste treatment and disposal can be troublesome.